PRTN3 and rheumatoid arthritis: In contrast to cigarette smoking, other pulmonary irritants like air pollution [39,40], organic dusts [41], asbestos [42,43], and silica [44] have been observed to be associated with increased risk not only of autoantibody-positive but also of autoantibody-negative RA, with only silica showing a strong association with ACPA-positive RA alone.